/Engine/Plugins/FX/Niagara/Source/Niagara/Classes/NiagaraGPUInstanceCountManager.h
Acquire an entry, this will either come from the free list or reallocate the buffer.
uint32 AcquireOrAllocateEntry ( [FRHICommandListImmediate](API\Runtime\RHI\FRHICommandListImmediate) & RHICmdList )